Direct Utilization of Plasma Proteins for the In Vivo Assembly of Protein-Drug/Imaging Agent Conjugates, Nanocarriers and Coatings for Biomaterials

ABSTRACT

The present invention includes compositions and methods for making and using a drug conjugated to a peptide or protein that binds specifically to a ligand in vivo, wherein the conjugate binds to its ligand in vivo and increases the half-life of the drug.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a Divisional application of U.S. patentapplication Ser. No. 12/649,941 filed on Dec. 30, 2009, which claimspriority to U.S. Provisional Patent Application Ser. No. 61/141,536,filed Dec. 30, 2008.

STATEMENT OF FEDERALLY FUNDED RESEARCH

None.

INCORPORATION-BY-REFERENCE OF MATERIALS FILED ON COMPACT DISC

None.

TECHNICAL FIELD OF THE INVENTION

The present invention relates in general to the field of in vivoassembly of conjugates, and more particularly, to compositions andmethods for the targeted delivery of active agents in in vivo.

BACKGROUND OF THE INVENTION

Without limiting the scope of the invention, its background is describedin connection with the delivery of active agents in vivo.

It is well known that low-molecular weight pharmaceutics are rapidlycleared from circulation following intravenous injection. This restrictsthe amount of time a therapeutically relevant dose can be maintained andgreatly limits the effectiveness of many of these compounds. A greatdeal of research has been conducted in an effort to prolong plasmaresidence times via conjugation to macromolecular constructs thatdisplay extended circulation profiles, such as polymers or proteins.However, these methods require the conjugation to be carried out exvivo.

One such method is taught in U.S. Pat. No. 7,344,698, issued to Lanza,et al., for Integrin targeted imaging agents. Briefly, this patentteaches emulsions of nanoparticles formed from high boiling liquidperfluorochemical substances, wherein the particles are coated with alipid/surfactant coating are made specific to regions of activatedendothelial cells by coupling said nanoparticles to a ligand specificfor α_(v)β₃ integrin, other than an antibody. The nanoparticles mayfurther include biologically active agents, radionuclides, or otherimaging agents.

Yet another example is U.S. Pat. No. 6,818,630, issued to Duncan, etal., for biologically active materials, particularly materials thatcomprise a biodegradeable polymer, linked to a biologically activeagent. The patent is said to teach materials known as polymer-drugconjugates that typically contain a therapeutic agent, for instance abioactive cytotoxic drug linked to a polymer backbone (the linkage istypically a convalent linkage). In some embodiments the disclosureconcerns other polymer conjugates including those where the biologicallyactive agent is an imaging agent, such as a tyrosinamide, a diagnosticagent, or a targeting agent, such as biotin.

Yet another example is U.S. Pat. No. 5,965,131, issued to Griffiths, etal., for the delivery of diagnostic and therapeutic agents to a targetsite. Briefly, this patent teaches improved in vivo pretargeting methodsfor delivering diagnostic or therapeutic agents to a target site in amammal uses a clearing agent that binds to the target-binding site ofthe targeting species, whereby non-bound primary targeting species iscleared from circulation but the clearing agent does not remove thebound primary targeting species. Anti-idiotype antibodies and antibodyfragments are preferred clearing agents. Fast clearance is achieved byglycosylating the clearing agent with sugar residues that bind to thehepatic asialoglycoprotein receptor.

SUMMARY OF THE INVENTION

In one embodiment, the present invention includes compositions andmethods for targeted drug delivery comprising: identifying a patient inneed of drug therapy; attaching a drug to a molecular recognitionelement to form a drug-molecular recognition element conjugate thatbinds specifically to a target in vivo, and treating the patient withthe conjugate, wherein the conjugate binds its ligand in vivo andincreases the half-life of the drug. In one aspect, the ligand comprisesa serum protein, a cell surface, a cancer, or a tissue. In anotheraspect, the drug and the molecular recognition element are conjugated bya biodegradable linker. In another aspect, the drug and the molecularrecognition element are conjugated by a cleavable linker. In anotheraspect, the drug and the molecular recognition element are conjugated bya stimuli-responsive cleavable linker. In another aspect, the molecularrecognition element binds to its ligand in vivo with an affinity greaterthan 100 nM. In another aspect, the molecular recognition element ismultimeric and generates plasma protein-based nanoparticles in vivo. Inanother aspect, the molecular recognition element directs assembly of aprotective protein coat to the surface of nanoparticles in vivo. Inanother aspect, the molecular recognition element binds a biomaterialsurface and directs protein opsonization to the biomaterials surface.

In another embodiment, the present invention includes a compositioncomprising a drug conjugated to a molecular recognition element thatbinds specifically to a ligand in vivo, wherein the conjugate binds toits ligand in vivo and increases the half-life of the drug. In anotherembodiment, the present invention includes a composition comprising adrug conjugated to a peptide or protein that binds specifically to aligand in vivo, wherein the conjugate binds to its ligand in vivo andincreases the half-life of the drug. In one aspect, the ligand comprisesa serum protein, a cell surface, a cancer, or a tissue. In anotheraspect, the drug and the molecular recognition element are conjugated bya biodegradable linker. In another aspect, the drug and the molecularrecognition element are conjugated by a cleavable linker. In anotheraspect, the drug and the molecular recognition element are conjugated bya stimuli-responsive cleavable linker. In another aspect, the molecularrecognition element binds to its ligand in vivo with an affinity greaterthan 100 nM. In another aspect, the molecular recognition element ismultimeric and generates plasma protein-based nanoparticles in vivo. Inanother aspect, the molecular recognition element directs assembly of aprotective protein coat to the surface of nanoparticles in vivo. Inanother aspect, the molecular recognition element binds a biomaterialsurface and directs protein opsonization to the biomaterials surface.

The present invention also include a composition and a method fortargeted drug delivery comprising: identifying a patient in need of drugtherapy; attaching a drug to a peptide or protein to form a drug-ligandbinding peptide or protein conjugate that binds specifically to a ligandin vivo; and treating the patient with the conjugate, wherein theconjugate binds its ligand in vivo and increases the half-life of thedrug. In yet another embodiment, the present invention includes acomposition and a method of making the composition for targeting aligand for delivery of a drug in vivo comprising identifying a ligand,isolating a ligand-specific molecular recognition element specific forthe ligand, wherein the molecular recognition element is capable ofbinding to the ligand in vivo, and attaching a drug to the molecularrecognition element. In one aspect, the ligand comprises a serumprotein, a cell surface, a cancer, or a tissue. In another aspect, thedrug and the molecular recognition element are conjugated by abiodegradable linker. In another aspect, the drug and the molecularrecognition element are conjugated by a cleavable linker In anotheraspect, the drug and the molecular recognition element are conjugated bya stimuli-responsive cleavable linker. In another aspect, the molecularrecognition element binds to its ligand in vivo with an affinity greaterthan 100 nM. In another aspect, the molecular recognition element ismultimeric and generates plasma protein-based nanoparticles in vivo. Inanother aspect, the molecular recognition element directs assembly of aprotective protein coat to the surface of nanoparticles in vivo. Inanother aspect, the molecular recognition element binds a biomaterialsurface and directs protein opsonization to the biomaterials surface.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the features and advantages of thepresent invention, reference is now made to the detailed description ofthe invention along with the accompanying figures and in which:

FIG. 1 shows the direct opsonization method of the present invention inwhich the opsonizing molecules are pre-attached to the surface usingdirect conjugation rather than random binding.

DETAILED DESCRIPTION OF THE INVENTION

While the making and using of various embodiments of the presentinvention are discussed in detail below, it should be appreciated thatthe present invention provides many applicable inventive concepts thatcan be embodied in a wide variety of specific contexts. The specificembodiments discussed herein are merely illustrative of specific ways tomake and use the invention and do not delimit the scope of theinvention.

To facilitate the understanding of this invention, a number of terms aredefined below. Terms defined herein have meanings as commonly understoodby a person of ordinary skill in the areas relevant to the presentinvention. Terms such as “a”, “an” and “the” are not intended to referto only a singular entity, but include the general class of which aspecific example may be used for illustration. The terminology herein isused to describe specific embodiments of the invention, but their usagedoes not delimit the invention, except as outlined in the claims.

The present invention can be used to target a wide variety of proteins,carbohydrates, lipids and combinations thereof for both the delivery andtargeting of the molecules.

As used herein, the term “antibody” refers to a protein produced by amammalian immune system that binds tightly and specifically toparticular molecules.

As used herein, the term “antigen” refers to a ligand that is boundspecifically by an antibody.

As used herein, the term “biodegradable” refers to degradation in abiological system, for example, enzymatic degradation or chemicaldegradation. For example, a biodegradable linker is a chemical moietythat is degradable under physiologic conditions and that upondegradation releases previously linked into individual molecularentities.

As used herein, the terms “drug,” “therapeutic,” or “active agent” referto any molecule, molecular complex or substance administered to anorganism for diagnostic or therapeutic purposes, including the treatmentof a disease or infection, medical imaging, monitoring, contraceptive,cosmetic, nutraceutical, pharmaceutical and prophylactic applications.The term “drug” includes any such molecule, molecular complex orsubstance that is chemically modified and/or operatively attached to abiologic or biocompatible structure. The term “prodrug” refers to adrug, drug precursor or modified drug that is not fully active oravailable until converted in vivo to its therapeutically active oravailable form. The term “prodrug complex” refers to a prodrugcomprising at least two noncovalently bound molecules and includes,without limitation, a drug specifically bound to a synthetic receptor.The term “multi-prodrug complex,” also described herein as a“multi-prodrug reservoir,” refers to a prodrug complex comprising atleast two drug molecules specifically bound to at least two syntheticreceptors.

As used herein, the terms “specifically bind,” “specifically bound” and“specific binding” refer to saturable, noncovalent interaction between aligand and a receptor that can be competitively inhibited by structuralanalogs of the ligand.

As used herein, the term “ligand” refers to any serum protein, hostcell, cell surface antigen, cell surface receptor, or host organ thatmay be used to be bound to the molecular recognition element in vivo.Other non-limiting examples of ligands include growth factors,cytokines, prosthetic groups, coenzymes, cofactors, regulatory factors,antigens, receptors, haptens, vitamins, nucleic acids and natural orsynthetic heteropolymers comprising amino acids, nucleotides,carbohydrates or non-biologic monomers, including analogs andderivatives thereof, and conjugates or complexes formed by attaching orbinding any of these molecules to a second molecule. Generally, theligands for the present invention are serum proteins.

As used herein, the term “receptor” refers to a specific binding partnerof a ligand and includes, without limitation, membrane receptors,soluble receptors, cloned receptors, recombinant receptors, hormonereceptors, drug receptors, transmitter receptors, autacoid receptors,cytokine receptors, antibodies, antibody fragments, engineeredantibodies, antibody mimics, molecular recognition units, adhesionmolecules, agglutinins, integrins, selectins, nucleic acids andsynthetic heteropolymers comprising amino acids, nucleotides,carbohydrates or non-biologic monomers, including analogs andderivatives thereof, and conjugates or complexes formed by attaching orbinding any of these molecules to a second molecule.

As used herein, the term “drug-ligand binding peptide conjugate” or“drug-ligand binding protein conjugate” refers to a molecule thatincludes two domains, one domain that binds specifically to a ligand invivo, and a second domain that includes a drug. For example, the presentinvention may include a drug-ligand binding peptide or protein conjugatethat includes an antibody or fragment thereof (e.g., a humanizedantibody fragment) that binds specifically to a serum protein (e.g.,Complement cascade proteins, albumin, LDL, HDL, VLDL) and that forms aconjugate in vivo that then helps deliver the drug to a target withinthe body. In one example, the drug-ligand binding peptide or proteinconjugate modifies the half-life of the drug (for example increases thehalf life) and can also increase the relative concentration of the drugat the target site.

As used herein, the term “molecular recognition element” refers tomolecules capable of specifically (i.e., non-randomly) binding to,hybridizing to, or otherwise interacting with a desired ligand molecule.Examples of molecular recognition elements include, but are not limitedto, polypeptides (e.g., antigen binding proteins, receptor ligands,signal peptides, hydrophobic membrane spanning domains), antibodies (andportions thereof), nucleic acid molecules (e.g., RNA and DNA, includingligand-binding RNA molecules), organic molecules (e.g., biotin,carbohydrates, glycoproteins), and inorganic molecules (e.g., vitamins).A given drug may be bound to one or more molecular recognition elements.

As used herein, the term “target” refers to cells, organs or theorganism in need to treatment with a drug or active agent. In certaincases, the target will be diseases cells, disease causing cells,autoimmune, microorganism, bacteria, virus, fungus, plant, protozoa, orpathogen or portion of an organism, cell, microorganism, bacteria,virus, fungus, plant, prion, protozoa or pathogen.

Other methods for screening ligands for protein binding can beenvisioned. Methods which are “low through-put” are less desirable thanhigh through-put ones such as a one-bead-one-compound (OBOC) peptidelibrary. Other methods are known for generating combinatorial peptidelibraries.

The present invention provides compositions and methods for enhancingimmune responses will likely be possible using methods outlined here.Many cancer types avoid immune recognition through tolerance mechanisms.This tolerance could be overcome by selectively tagging proteins on thesurface of cancer cells with stimulatory signals for the immune system,such as tagging with non-specific IgG.

EXAMPLE 1 Novel Small-Molecule Conjugates Capable of Binding with HighAffinity to Plasma Proteins

Low-molecular weight pharmaceutics are rapidly cleared from circulationfollowing intravenous injection. Rapid clearing restricts the amount oftime a therapeutically relevant dose can be maintained and greatlylimits the effectiveness of many of these compounds. A great deal ofresearch has been conducted in an effort to prolong plasma residencetimes via conjugation to macromolecular constructs that display extendedcirculation profiles, such as polymers or proteins. Prior art methodsalmost exclusively require the conjugation to be carried out ex vivo. Anin vivo method is more desirable, and this embodiment of the inventionencompasses a method for attaching the low molecular weight therapeuticsto specific proteins in vivo to extend their plasma half-lives. Theconjugate includes a molecular recognition element (e.g., a protein orpeptide that specifically binds to a ligand in vivo) specific for adesired plasma protein and a therapeutic. For example, a ligand thatbinds non-covalently to albumin with high-affinity and selectivity iselucidated by using a one-bead-one-compound (OBOC) peptide library usedto find molecular recognition elements (also referred to herein astargeting ligands) for, e.g., cancer cells. A high-affinity ligand islinked to a therapeutic molecule through either a degradable ornon-degradable linker. When administered by intravenous injection, thisconjugate should selectively bind to albumin in circulation, whichreduces the rate of clearance of the therapeutic. Two aspects of theconjugate are important: 1) choice of ligand protein—a wide variety ofplasma proteins can be targeted including: albumin, transferrin, as wellas proteins expressed on the surface of red blood cells, etc., with theidentity of the ligand protein altering the biodistribution of thetherapeutic and engendering the ability to target specific cells ortissues, 2) the release of the therapeutic can be facilitated by eithertailoring the affinity of the molecular recognition element or targetingligand for it's ligand to achieve the desired release rate profile or byincorporating a stimuli-responsive linker between the molecularrecognition element and the drug, therapeutic or active agent.

EXAMPLE 2 Nanoparticles Assembled in Vivo

Conjugates described in example 1 in which the targeting ligand is mademultimeric are used to generate plasma protein-based nanoparticles invivo. Therapeutics contained in these nanoparticles can displaysignificantly different biodistribution profiles compared to freetherapeutic or even conjugates from example 1. Release of therapeutic isachieved as outlined in example 1.

EXAMPLE 3 Directed Assembly of a Protective Protein Coat to the Surfaceof Nanoparticles in Vivo

Plasma protein targeting ligands such as those described in example 1are conjugated to the surface of nanoparticles to facilitate the bindingof target proteins to the surface of the particle upon intravenousinjection. The proteins bound as a result of binding camouflage theparticle and reduce particle recognition by cells of the immune system,such as macrophages, thereby extending the circulation time of thenanoparticle.

EXAMPLE 4 Directed Protein Opsonization to Biomaterials Surfaces

Custom-tailored materials find widespread use in drug delivery, tissueengineering, bioanalytical chemistry, and implantable medical devices.Despite their widespread use, a detailed understanding of how thesematerials interact with living systems is still lacking When a materialis introduced to the body, a complex series of events ensue beginningwith protein adsorption to the surface of the material (opsonization),which leads either to local inflammation or to sequestration of thematerial by cells of the immune system. In the case of an implantedmaterial, the foreign body response (FBR) universally occurs. Thisresponse begins with opsonization, which leads to inflammation andultimately to encapsulation of the material in a dense fibrous coat.Macrophages, a sub-set of leukocytes, play an important role in FBR.When they encounter an implanted material, they remain at the wound siteindefinitely eventually fusing together to form foreign body giant cells(FBGC) at the material/tissue interface. These cells, observedexclusively during FBR, release toxic and inflammatory compounds at thewound site.

Opsonization plays a central role in the activation of the immunesystem. It begins immediately after a material comes in contact withplasma. The exact nature of the types and quantities of proteins, andtheir conformations, dictate the body's reaction to the material. It istherefore paramount that this process be harnessed and used toorchestrate desired outcomes based on application-specific requirements.The mechanisms involved are not well understood; however, the majoropsonins are known. Immunoglobulin and complement proteins are thepredominant contributors to the recognition of foreign materials bymacrophages. Immunoglobulin adsorbed to the surface binds to macrophagesthrough an Fc receptor on the macrophage. This attachment results inadherence to the material and possibly to internalization depending onthe size of the material relative to that of the cell. Adsorption ofcomplement protein C3 can induce conformational changes in the protein'sstructure that activate it toward cleavage to C3b. Macrophages express areceptor to C3b (CR1), which again facilitates attachment to thematerial.

FIG. 1 shows the direct opsonization method of the present invention inwhich the opsonizing molecules are pre-attached to the surface usingdirect conjugation rather than random binding.

This example of the invention describes the elucidation of peptide-basedligands capable of high-affinity binding to specific plasma proteinslike those described in example 1. These ligands, when immobilized onthe surfaces of biomaterials, direct protein adsorption in vivo. Forexample, a high-affinity peptide ligand for albumin bound to the surfaceof a material adsorbs albumin upon exposure to plasma (albumin makes up˜60 of blood protein). Similarly, a material coated with a high-affinitypeptide ligand for transferrin will bind that protein when exposed toplasma. Using this method controls which proteins adsorb to the surfaceof biomaterials, and in what proportions.

Methods used extensively in the search for cancer targeting ligands areemployed to identify short peptide sequences capable of binding tovarious plasma proteins. Using a one-bead-one-compound (OBOC) library,1×10⁴−1×10⁸ individual peptide sequences are generated via traditionalsolid-phase peptide synthesis (TantaGel S NH₂ resin, 130 μm). A4-hydroxymethylbenzoic acid resin linker is used to facilitatesequencing via MALDI-TOF mass spec analysis. Beads are screened forbinding to the desired fluorescently-labeled protein. Positive hits willbe identified via fluorescence microscopy, removed from solution using amicro-pipette, and analyzed by mass spec. A batch of beads with onlythis peptide on the surface is synthesized. These beads are incubatedwith plasma and the identities of bound proteins determined via standardmethods.

This invention makes possible the in vivo recruitment of proteins to thematerial surface that can be used to dictate the body's response to thematerial. Vascular endothelial growth factor (VEGF) can be recruited topromote wound healing and ligands capable of binding to inhibitoryreceptors expressed by macrophages will be used to decrease inflammationnear the biomaterial surface. Cell-type specific ligands will be used topromote selective colonization of the biomaterial surface.

It is contemplated that any embodiment discussed in this specificationcan be implemented with respect to any method, kit, reagent, orcomposition of the invention, and vice versa. Furthermore, compositionsof the invention can be used to achieve methods of the invention.

It will be understood that particular embodiments described herein areshown by way of illustration and not as limitations of the invention.The principal features of this invention can be employed in variousembodiments without departing from the scope of the invention. Thoseskilled in the art will recognize, or be able to ascertain using no morethan routine experimentation, numerous equivalents to the specificprocedures described herein. Such equivalents are considered to bewithin the scope of this invention and are covered by the claims.

All publications and patent applications mentioned in the specificationare indicative of the level of skill of those skilled in the art towhich this invention pertains. All publications and patent applicationsare herein incorporated by reference to the same extent as if eachindividual publication or patent application was specifically andindividually indicated to be incorporated by reference.

The use of the word “a” or “an” when used in conjunction with the term“comprising” in the claims and/or the specification may mean “one,” butit is also consistent with the meaning of “one or more,” “at least one,”and “one or more than one.” The use of the term “or” in the claims isused to mean “and/or” unless explicitly indicated to refer toalternatives only or the alternatives are mutually exclusive, althoughthe disclosure supports a definition that refers to only alternativesand “and/or.” Throughout this application, the term “about” is used toindicate that a value includes the inherent variation of error for thedevice, the method being employed to determine the value, or thevariation that exists among the study subjects.

As used in this specification and claim(s), the words “comprising” (andany form of comprising, such as “comprise” and “comprises”), “having”(and any form of having, such as “have” and “has”), “including” (and anyform of including, such as “includes” and “include”) or “containing”(and any form of containing, such as “contains” and “contain”) areinclusive or open-ended and do not exclude additional, unrecitedelements or method steps.

The term “or combinations thereof” as used herein refers to allpermutations and combinations of the listed items preceding the term.For example, “A, B, C, or combinations thereof” is intended to includeat least one of: A, B, C, AB, AC, BC, or ABC, and if order is importantin a particular context, also BA, CA, CB, CBA, BCA, ACB, BAC, or CAB.Continuing with this example, expressly included are combinations thatcontain repeats of one or more item or term, such as BB, AAA, AB, BBC,AAABCCCC, CBBAAA, CABABB, and so forth. The skilled artisan willunderstand that typically there is no limit on the number of items orterms in any combination, unless otherwise apparent from the context.

All of the compositions and/or methods disclosed and claimed herein canbe made and executed without undue experimentation in light of thepresent disclosure. While the compositions and methods of this inventionhave been described in terms of preferred embodiments, it will beapparent to those of skill in the art that variations may be applied tothe compositions and/or methods and in the steps or in the sequence ofsteps of the method described herein without departing from the concept,spirit and scope of the invention. All such similar substitutes andmodifications apparent to those skilled in the art are deemed to bewithin the spirit, scope and concept of the invention as defined by theappended claims.

REFERENCES

Aina, O. H.; Liu, R. W.; Sutcliffe, J. L.; Marik, J.; Pan, C. X.; Lam,K. S., From combinatorial chemistry to cancer-targeting peptides.Molecular Pharmaceutics 2007, 4, (5), 631-651.

Castner, D. G.; Ratner, B. D., Biomedical surface science: Foundationsto frontiers. Surface Science 2002, 500, (1-3), 28-60.

Kratz, F.; Warnecke, A.; Scheuermann, K.; Stockmar, C.; Schwab, J.;Lazar, P.; Druckes, P.; Esser, N.; Drecs, J.; Rognan, D.; Bissantz, C.;Hinderling, C.; Folkers, G.; Fichtner, I.; Unger, C. “Probing thecysteine-34 position of endogenous serum albumin with thiol-bindingdoxorubicin derivatives. Improved efficacy of an acid-sensitivedoxorubicin derivative with specific albumin-binding properties comparedto that of the parent compound” J. Med. Chem., 2002, 45, 5523-5533.

Kratz, F.; Muller, I. A.; Ryppa, C.; Warnecke, A., Prodrug strategies inanticancer chemotherapy. Chem Med Chem 2008, 3, (1), 20-53.

Liu, L. Y.; Chen, G.; Chao, T.; Ratner, B. D.; Sage, E. H.; Jiang, S.Y., Reduced foreign body reaction to implanted biomaterials by surfacetreatment with oriented osteopontin. Journal of BiomaterialsScience-Polymer Edition 2008, 19, (6), 821-835.

Moghimi, S. M.; Hunter, A. C.; Murray, J. C., Long-circulating andtarget-specific nanoparticles: theory to practice. Pharmacol Rev 2001,53, (2), 283-318.

What is claimed is: 1-9. (canceled)
 10. A composition comprising a drugconjugated to a molecular recognition element that binds specifically toa ligand in vivo, wherein the conjugate binds to its ligand in vivo andincreases the half-life of the drug.
 11. The composition of claim 10,wherein the ligand comprises a serum protein, a cell surface, a cancer,or a tissue.
 12. The composition of claim 10, wherein the drug and thebinding peptide or protein are conjugated by a biodegradable linker. 13.The composition of claim 10, wherein the drug and the binding peptide orprotein are conjugated by a cleavable linker.
 14. The composition ofclaim 10, wherein the drug and the binding peptide or protein areconjugated by a stimuli-responsive cleavable linker.
 15. The compositionof claim 10, wherein the binding peptide or protein binds to its ligandwith an affinity greater than 100 nM.
 16. The composition of claim 10,wherein the binding peptide or protein is multimeric and generatesplasma protein-based nanoparticles in vivo.
 17. The composition of claim10, wherein the binding peptide or protein directs assembly of aprotective protein coat to the surface of nanoparticles in vivo.
 18. Thecomposition of claim 10, wherein the binding peptide or protein binds abiomaterial surface and directs protein opsonization to the biomaterialssurface.
 19. A composition comprising a drug conjugated to a peptide orprotein that binds specifically to a ligand in vivo, wherein theconjugate binds to its ligand in vivo and increases the half-life of thedrug.
 20. The composition of claim 19, wherein the ligand comprises aserum protein, a cell surface, a cancer, or a tissue.
 21. Thecomposition of claim 19, wherein the drug and the binding peptide orprotein are conjugated by a biodegradable linker.
 22. The composition ofclaim 19, wherein the drug and the binding peptide or protein areconjugated by a cleavable linker.
 23. The composition of claim 19,wherein the drug and the binding peptide or protein are conjugated by astimuli-responsive cleavable linker.
 24. The composition of claim 19,wherein the binding peptide or protein binds to its ligand with anaffinity greater than 100 nM.
 25. The composition of claim 19, whereinthe binding peptide or protein is multimeric and generates plasmaprotein-based nanoparticles in vivo.
 26. The composition of claim 19,wherein the binding peptide or protein directs assembly of a protectiveprotein coat to the surface of nanoparticles in vivo.
 27. Thecomposition of claim 19, wherein the binding peptide or protein binds abiomaterial surface and directs protein opsonization to the biomaterialssurface. 28-37. (canceled)
 38. A composition made by the methodcomprising: selecting a ligand for targeting the delivery of a drug invivo comprising identifying a ligand, isolating a ligand-specificmolecular recognition element specific for the ligand, wherein themolecular recognition element is capable of binding to the ligand invivo, and attaching a drug to the molecular recognition element.